Field
This disclosure relates to electrical system testing and particularly to testing electrical power distributions systems for intermittent faults.
Description of the Related Art
Electronic systems are ubiquitous. An essential component of these systems is their internal signal paths, most typically provided by wired interconnects. Failures in the wiring frequently result in failure of the system. For example, aging wiring in buildings, aircraft and transportation systems, consumer products, industrial machinery, and the like is among the most significant potential causes of catastrophic failure and maintenance cost in these structures. High profile airline crashes attributed to aging wiring have brought the need for improved wire testing systems to the forefront of industry attention.
Various techniques for the characterization and fault detection of electronic signal paths are known. For example, techniques such as time domain reflectometry (TDR), frequency domain reflectometry (FDR), and sequence time domain reflectometry (STDR) can be used to determine where a short or break in a wire has occurred. More recently, improvements such as spectral time domain reflectometry (STRDR) and spread spectrum time domain reflectometry (SSTDR) have been developed to allow testing of a wire while operational signals are present. Common to all of these techniques is the injection of a reflectometry test signal into the wire to be tested, and observation of the response. As the test signal propagates from the test instrument, impedance mismatches in the wire generate reflections that propagate back to the test instrument. Impedance mismatches can be caused by a variety of things, including for example, breaks in the wire, short circuits, branches, and wire gauge changes. The resulting response can be analyzed to determine features of the wire, such as distance to an open or short circuit.
Traditionally, reflectometry has been a form of off-line testing, since on-line live testing was avoided because the test signal may interfere with the existing power and/or signals on the line, and vice versa. Unfortunately, certain types of failures, such as an intermittent open-circuit or short-circuit, are difficult to detect off-line, since the conditions causing the failure are often not present during off-line testing.
Throughout this description, elements appearing in figures are assigned three-digit reference designators, where the most significant digit is the figure number where the element is introduced and the two least significant digits are specific to the element. An element that is not described in conjunction with a figure may be presumed to have the same characteristics and function as a previously-described element having the same reference designator.